Reducing and Enlarging Formulas Yewande Dayo Student Pharmacist

Objectives Perform calculations to reduce and enlarge formulas for pharmaceutical preparations stated in metric quantities Perform calculations to reduce and enlarge formulas for pharmaceutical preparations stated in proportional parts

Reducing and Enlarging Formulas Official USP-NF formulas are generally based on preparing 1000 mL or 1000g of product. Some formulas are based on the preparation of a dosage unit (e.g. 1 capsule) or other quantity (e.g. 100 mL). Industrial formulas may be scaled up to quantities of ingredients necessary to make hundreds of thousands of dosage units in a production batch. Thus, quite frequently, Pharmacists have to reduce or enlarge formulas in their course of practice This may be calculating the quantities of each ingredient required for a smaller or greater quantity while maintaining the correct proportion of one ingredient to the other. It is important to maintain the proportion of one ingredient to the other

Reducing or enlarging formulas can be done by a two- step process: Determine the factor that defines the multiple or the fraction of the amount of formula to be prepared Factor = Quantity of formula desired/ quantity of formula given Multiply the quantity of each ingredient in the formula by the factor to determine the amount of each ingredient required in the reduced or enlarged formula A factor greater than 1 represents the multiple of the formula, and a factor less than 1 indicates the fraction of the formula

Example 1 If a formula for 1000 mL contains 6 g of a drug, how many grams of drug are needed to prepare 60 mL of the formula 60 mL/1000 mL = 0.06 (factor) 6 g x 0.06 = 0.36 g, answer

Example 2 RX Zinc oxide 50 g Pine tar 120 g Petrolatum 284 g How much pine tar would be required to prepare 1 kg of the ointment? Factor = 1000 g/454 g = 2.2 Amount of pine tar required = 120 x 2.2 = 264 g

Example 3 RX Zinc oxide 50 g Pine tar 120 g Petrolatum q.s. ad. 284 g How much pine tar would be required to prepare 1 kg of the ointment? Factor = 1000/284 = 3.5 Amount of pine tar required = 3.5 x 120 = 420 g

Example 4 From the following formula, calculate the quantity of each ingredient required to make 240 mL of calamine lotion. Calamine 80 g Zinc oxide 80 g Glycerin 20g Bentonite magma 250 mL Ca(OH)2 solution to make 1000 mL Calamine: 19.2 g, Zinc Oxide: 19.2 g, Glycerin: 4.8 mL, bentonite magma: 60 mL, calcium hydroxide qs to make 240 mL

Example 5 From the following formula for artificial tears, calculate the quantity of each ingredient required to prepare a dozen 30 mL container Polyvinyl Alcohol 1.4 g Povidone 0.6 g Chlorobutanol 0.5 g Sterile Sodium Chloride Solution, 9% ad 100 mL Polyvinyl: 5.04 g, Povidone: 2.16 g, Chlorobutanol: 1.8 g, 9% NS ad 360 mL

Formulas That Specify Proportional Parts Rarely, a pharmacist may encounter an old formula with ingredients in “parts” rather than measures of weight and volume The “parts” indicate a relative proportion of each ingredient in weight or volume

Example 6 RX Coal Tar 5 parts Zinc Oxide 10 parts Hydrophilic Ointment 50 parts Calculate the quantity of each ingredient to make 1000g of the ointment. Total parts by weight = 65 Thus, 1000 g will contain 65 parts!!! Coal tar: 76.92 g, Zinc Oxide: 153.85 g, hydrophilic ointment: 769.23 g, make sure it adds up to 1000g